The present disclosure relates to a mobile communication system, and more specifically, to a group control in a mobile communication system.
In a mobile communication system, each base station transmits or receives data to or from a plurality of terminals through one cell/sector in a wireless channel environment. In a system operated using multiple carriers or the like, a base station receives packet traffic from a wired Internet network and transmits the received packet traffic to each terminal using a predetermined communication protocol.
In this case, downlink scheduling includes determination as to when the base station transmits data, to which terminal the data is transmitted, and which frequency region is used for data transmission. In addition, the base station receives and demodulates data from the terminal using a predetermined communication protocol and transmits packet traffic through a wired Internet network. On the other hand, uplink scheduling includes determination as to when uplink data is transmitted to the base station, which terminal transmits the uplink data, and which frequency band is used for uplink data transmission. In general, scheduling is performed such that a terminal with a good channel status transmits or receives data using more time and frequency resources.
FIG. 1 is a diagram illustrating time-frequency resource blocks.
A resource used for communication in a system operated using multiple carriers or the like may be divided into a time domain and a frequency domain. The resource may be defined by resource blocks (RBs) and each RB includes N subcarriers and M subframes or a predetermined time unit. Here, N and M may be 1.
One rectangle shown in FIG. 1 denotes one RB, and one RB includes at least one subcarrier located on one axis and a predetermined time unit located on the other axis. In downlink, the base station selects a terminal according to a predetermined scheduling rule, allocates one or more RBs to the selected terminal, and transmits data to the selected terminal using the allocated RBs.
In uplink, the base station selects a terminal and allocates one or more RBs to the selected user equipment according to predetermined scheduling rule. The terminal receives scheduling information indicating that the base station has allocated certain RBs to the terminal and transmits uplink data using the allocated RBs.
In the downlink scheduling scheme, the base station selects time-frequency RBs with a good channel status based on a downlink channel quality indicator (CQI) reported by the terminal and transmits data using the selected RBs. Since the time-frequency RBs with the good channel status are used, it is possible to transmit a larger amount of data while using restricted RBs. Thus, it is possible to increase overall data transfer capacity of the system. In the uplink scheduling scheme, a scheduler of the base station may measure the reception status of a pilot signal (or reference signal) transmitted from the terminal and select time-frequency RBs with a good uplink channel status. The scheduler of the base station may allocate the selected RBs to the user equipment, and the terminal may transmit uplink data using the allocated RBs.
The scheduling described above may be performed on a group basis.
Hereinafter, a group resource allocation method will be described in brief.
Group Resource Allocation (GRA)
Group resource allocation (GRA) method is a method for allocating resources to a plurality of users (i.e., terminals) belonging to one group in order to reduce overhead of control messages that a base station transmits to the terminals. Using the GRA method, it is possible to reduce signaling overhead in a network since the base station can compress and transmit control information, of which the base station informs terminals, on a group by group basis when individually allocating resources to the terminals.
The base station can use group control information for configuring and allocating resources to one or more terminals belonging to one group.
Here, the group control information may be referred to as an advanced MAP or “A-MAP. Multiple information elements are individually coded in the A-MAP associated with user specific control information of a single user or a user group. In the A-MAP, an ID of each terminal (for example, a station identifier (STID) of a specific terminal, a broadcast STID, and/or a multicast STID) is CRC-masked to be transmitted.
Since the A-MAP is individually encoded and masked with an STID, each terminal performs blind decoding of a region in which the A-MAP is transmitted in order to check whether or not an A-MAP destined for the terminal exists.
In this case, the terminal can detect the A-MAP using an STID, a broadcast STID, and/or a multicast STID (for example, a group ID, a persistent ID, a sleep/idle mode ID, or an MBS ID).
The terminal performs blind decoding based on a MAP size used in a corresponding system. In this case, the base station and/or the terminal may limit the size and type of the MAP to specific sizes and types so as to reduce the number of blind decodings.
For example, the base station and/or the terminal may limit the size of the A-MAP information element (IE) to three sizes such as 56 (or 64), 96, and 144 bits or to two sizes such as 56 (or 64) and 96.
It is assumed that one minimum A-MAP logical resource unit (MLRU) includes 48 data subcarriers, two MLRUs include 96 data subcarriers, and the size of the A-MAP IE is determined to be 56 or 96. In this case, the base station may transmit each A-MAP IE to the terminal by mapping a 56-bit A-MAP IE to 1 MLRU and mapping a 96-bit A-MAP IE to 2 MLRUs using an encoding method used for a downlink control channel (for example, using a tail-biting convolutional code (TBCC) or puncturing method).
In a case where the UL MIMO mode set is ‘0b10’ in conventional group resource allocation, Mode 2 (i.e., CL SU-MIMO (SM)) is used. Here, Mt=1 (the number of streams that a terminal can have) and TNS (total number of streams)=2.
However, the TNS cannot be set to 2 in the CL SU-MIMO mode. This is because the TNS is the total number of streams used in uplink MU-MIMO (CSM).